A newly discovered fossil shows that within just 3 million years of their first appearance on Earth, ichthyosaurs had evolved into 17-metre-long giants
23 December 2021
Fossil remains of one of the ocean’s earliest giants have been unearthed in Nevada. Named Cymbospondylus youngorum, this ichthyosaur had a 2-metre-long skull and may have stretched around 17 metres in length.
Lars Schmitz at the W.M. Keck Science Department in California, a member of the team that analysed the remains, describes it as a “jaw-dropping” find.
Ichthyosaurs were marine reptiles that lived between about 249 million and 90 million years ago and had a body shape reminiscent of modern whales and dolphins. Some grew large, and C. youngorum was comparable in size to a modern sperm whale.
It was discovered in roughly 246 million-year-old rocks, so it is only about 3 million years younger than the first ichthyosaurs, which evolved from land-based ancestors. This indicates that ichthyosaurs ballooned in size astonishingly quickly once they took to the seas.
Neil Kelley at Vanderbilt University in Nashville, Tennessee, who wasn’t involved in the study, notes that fragments of such early giants have been found before, but says it’s “very exciting” to finally see more complete remains.
While many whale species have reached giant sizes in today’s seas, their evolutionary route was long. The earliest whales evolved about 56 million years ago and it took another 50 million years for some species to become enormous. C. youngorum shows that ichthyosaurs did the same in a fraction of the time, which underscores different evolutionary pathways for these superficially similar animals.
“By considering completely extinct animals like ichthyosaurs, we can develop a much richer picture of complexity and commonalities across the history of life,” says Kelley.
The ecosystem that hosted C. youngorum wasn’t like the seas today. “The food chains were shorter,” says Schmitz, with a proliferation of creatures, including ancient squid relatives called ammonoids, that would have provided ample sustenance for marine reptiles.
The glut of seafood allowed large ichthyosaurs to evolve and sustain themselves. Based on models of energy flow through the ancient food web, Schmitz notes that another giant-size ichthyosaur species could have survived in the same environment. Whales didn’t get the benefit of such a surfeit, and so took a much longer path to becoming leviathans.
Journal reference: Science, DOI: 10.1126/science.abf5787
Sign up to Wild Wild Life, a free monthly newsletter celebrating the diversity and science of animals, plants and Earth’s other weird and wonderful inhabitants
More on these topics: